1. Field of the Invention
The present invention relates to a laser apparatus for medical treatment use particularly for treating a birthmark or the like and, more particularly, relates to a laser medical treatment apparatus in which a giant pulse that is most effective for the treatment of a deep birthmark is outputted by using such techniques as the Q-switching method.
2. Description of the Related Art
Medical treatment of birthmarks by utilizing laser beams are effected by destroying an abnormal tissue such as melanophore in a skin of a human body, for example, which causes the birthmark. The principle of this treatment is that, by irradiating a laser beam having a wavelength which will not be well absorbed by normal tissues but will be absorbed at a higher rate by the abnormal tissue, the abnormal tissue may be destroyed while holding damage to the normal tissues to a minimum.
FIGS. 11 and 12 show conventional examples of a hand piece of a laser apparatus for medical treatment use, called laser medical treatment apparatus hereinafter, employed in such treatment of birthmarks. In the hand piece shown in FIG. 11, a laser beam LB delivered from a laser generator, for example by way of a mirror joint, is focused by means of a first lens 100 and it is then incident upon a uniform light irradiation member (known commercially as "KALEIDOSCOPE", Trade Name of Toshiba Corporation) 101 which has an axially extended cavity having a predetermined diameter. By means of this uniform light irradiation member 101, the laser beam of a circular Gaussian distribution is converted to have an angular uniform output distribution. This uniform output beam is further irradiated on a skin surface to be subjected to the medical treatment through a second lens 102. On the other hand, the hand piece shown in FIG. 12 is the one with more emphasis on its simplicity of construction than uniform light irradiation of FIG. 11, and the laser beam LB is focused by simply using a lens 103. The area of irradiation is varied by adjusting the distance from the lens 103. Both of these hand pieces use a beam spreading portion after the light converging point F of the laser beam and are constructed to have the uniform light irradiation member or to adjust the location of treatment, i.e. portion of a skin surface to be treated.
If, however, the above described conventional hand pieces are applied to a laser medical treatment apparatus which outputs a giant pulse by means of such techniques as the Q-switching method, the peak power of laser reaches a very high value such as several tens of MW or more. An air breakdown or the so-called laser discharge occurs at the converging position (focus) F of the laser beam and in the vicinity thereof so as to absorb the laser energy. Thus, there has been a problem that the energy at the treatment skin surface is significantly reduced. In other words, since an energy necessary for the aimed treatment is not obtained, the treatment of a deep birthmark is difficult because the laser beam cannot penetrate deeply inside the skin.
On the other hand, it is supposedly possible with a lens-type hand piece (structure shown in FIG. 12) to use the lens 103 having a relatively large focal length so that the treatment surface may be set on the lens side of the beam converging point F in order to avoid a laser discharge. However, in this method, if the laser is erroneously emitted into the air, the laser beam is converged (up to the beam converging point F) as it travels farther from the specified treatment surface. Since the energy density thereof becomes larger, a problem in safety operation will be raised even if protective glasses are worn.